Changes in the phase composition of a multicomponent Co-Mo-Bi-Fe-Sb-K-O catalyst under conditions of the partial oxidation of isobutylene to methacrolein: A comparison with the oxidation of propylene to acrolein

Abstract

The partial oxidation of isobutylene to methacrolein on a multicomponent multiphase Co-Mo-Bi-Fe-Sb-K-O catalyst and on catalysts from which some components were absent was studied. Activity and selectivity changes in the case of isobutylene oxidation were the same as in the oxidation of propylene; however, the rate of propylene oxidation was higher than that of isobutylene oxidation. The X-ray diffraction analysis of the catalysts before and after the reaction indicated the occurrence of a number of phases in the samples: α-CoMoO4, β-CoMoO4, Fe2(MoO4)3, reduced bismuth molybdate species, MoO3, and reduced MoO x species. Under catalytic reaction conditions, redox phase transformations occurred. Iron molybdate and molybdenum oxide phases underwent the largest transformations. Of two molybdenum oxide phases, a β-Mo4O11 phase with a structure of a crystallographic shift is formed in the course of catalysis, whereas the second phase (MoO3) almost does not participate in catalysis and occurs in an excess.